Separating constituents of coke oven gases



April 11, 1950 P. E. HAYNES 2,503,265

' ssmmms consn'rusms 0F com ovm GASES Filed July 25, 1946 cox: Oven GAS INVENTOR. 1 25:25 J90f/VA'6. MW

Patented Apr. 11, 1950 SEPARATING CONSTITUENTS OF COKE OVEN GASES Pierre Evan Haynes, Indianapolis, Ind., assignor to Koppers Company, Inc., Pittsburgh, Pa., a

corporation of Delaware Application July 23, 1946, Serial No. 685,654

12 Claims. 1

This invention relates to the separation of the constituents of coke oven gas. More particularly the invention relates to the separation and recovery of ethylene and propylene from coke oven gas.

The average olefine content of coke oven gas is approximately 3% by volume. Of this 3% of olefines approximately 80% is ethylene and 20% is propylene and butylene. Heretofore coke oven gas has not been treated for the recovery of these low percentages of olefines unless the high percentage of hydrogen in the gas may be recovered and used in such a manner as to absorb a considerable portion of the expense of separating the hydrogen and olefines from the gas.

I have found that Hz with CO, N2 and CH4 may be separated from coke oven gas as a single gas fraction. When this is done, the temperature at which the olefines may be recovered is considerabl higher on an average than the temperature at which the hydrogen may be recovered from coke oven gas as a separate product. This gas mixture fraction may be expanded in an expansion engine to provide cooling for separation of the gas and to provide work for the compression of the gas. The apparatus for carrying out this process is quite simple and the work required for effecting the expansion is comparatively low so that the olefines may be effectively and economically separated from coke oven gas.

The primary object of the present invention is to provide a method of and apparatus for separating olefines from coke oven gas b partial liquefaction of the gas wherein the low boiling constituents may be separated as a single fraction.

Another object is to provide a method of and apparatus for separating olefines from coke oven gas by liquefaction wherein the low boiling constituents may be separated as a single fraction and used for cooling in the rectification of the liquid products recovered to demethanize the liquid products. I

With these and other objects in view the invention consists in the method and apparatus for separating olefines from coke oven gas as hereinafter described and particularly defined in the claims.

The various features of the invention are illustrated in the accompanying drawing which is a diagrammatic flow sheet of an apparatus in which the preferred method of separating olefines from coke oven gas may be carried out, I

Coke oven gas which previously has been freed from carbon dioxide, benzene and other high boiling constituents is introduced through a line In into a compressor l2. The compressed gas flows through a line l4 into a line l8. The major portion of the purified coke oven gas is introduced through a line l6 into a compressor l9 which de livers compressed gas into the line I8. The gas is preferably compressed to a pressure of 12 to 25 atmospheres in the compressors l2 and I9 and then passed through a line l8 to a division point 20 where part of the gas flows through a line 22 into an evaporator 24, and then passes through a line 26 and into an evaporator 28 to be cooled and partially condensed in the evaporator. As the gas passes through the line l8, preferably methanol is introduced through a line 30 and valve 32 to prevent the compressed gas from forming hydrates with water in the gas as itis cooled in the evaporators 24 and 2-8. The gas passing through the evaporators 24 and M!' is cooled by expanded liquid hydrocarbons as hereinafter explained and then flows through a line 34 and control valve 36 into an interchange condenser 38.

Another portion of the compressed coke oven gas flows through a line 40, valve 42 and line 44 into the tubular section of a heat exchanger 46. From the top of the exchanger the gas passes through a line 48 and control valve 50 into the interchanger 38.

A third portion of the compressed coke oven gas flows from a division point 52 through a line 54 into a tubular coil 56 mounted in the base of'a rectifying column 5-8. From the tubular section 56 the'gas flows through a series of coils 60, 62, 64 and 66 which are distributed throughoutthe major portion of the height of the column for the purpose of heating or boiling liquid materials in the column and being cooled thereby. The cooled products pass from the last coil 66 through a line 68 and control valve 10 into the interchanger 38.

Most of the C2 and higher boiling hydrocarbons are condensed in separator 38, along with methane, under the influence of cooling which is provided by cold residue gases passing through the exchanger as hereinafter described. Baflles "12 are arranged within the exchanger '38 which form trays and assist in rectifying the condensed material therein to separate the hydrogen, nitrogen, carbon monoxide and part of the methane from the higher boiling hydrocarbons which are condensed. The liquefied higher boiling material is conducted from the base of the exchanger" through a line 14 and passes through a sprayhead It into the top of the column 58. The column 58 is preferably a bubble cap column with the interchange coils arranged between the trays of bubble caps. The incoming compressed gas introduced through the line 54 acts to heat liquid accumulating in the lower portion of the column mixture.

To assist in the rectification, a condenser I8 is mounted on the top or the tower 58 and is provided with a series of tubes 80 through which the vapors from the tower circulate. The outside of the tubes 80 is cooled by cold gases which flow into the condenser from the interchanger 38 through a line 82. The gases passing throu the line 82 are composed principally of hydrogen, nitrogen, carbon monoxide and some methane. These gases leave the top of the interchanger 38 which is' the coldest part thereof, after being cooled by an indirect heat interchange with cooled gases from an expansion engine which have an average temperature of approximately 116 K., that is the temperature may vary from 110 to 124 K. The cooled gases circulated through the condenser 18 act to condense and reflux the higher boiling vapors passing up into the tubes 80 and thus materially assist in the rectification of the liquefied gas. In operation the rectification is carried out to the point that only methane flows through an outlet 84 of the condenser and all of the methane is removed from the liquid reaching the bottom of the tower. The liquid reaching the bottom of the tower is removed through a line 86 and is composed of ethylene, propylene, a small amount of butylene, ethane and possibly some propane. a

The cooling gases circulated through the condenser 18 leave the bottom oi the condenser through a line 88 and are mixed with methane fiowing through the line 84 and a valve 90. This mixture of cold non-condensed gases then passes through an adiabatic expansion engine 92 in order to cool the gases. The gas mixture entering the expansion engine has an average temperature of 136 K. and exhausts therefrom at an average temperature of 115 K. This cold gas flows through a line 93 into the top of interchanger 38, then passes through the interchangers 38 and 48 to cool the incoming gas. The work done by expansion engine 92 is imparted to the first stage compressor I2 and is utilized in compressing the raw gas used in the process. This expansion engine is important in this process in that it provides a cold cooling medium that will permit the liquefaction of the gas being treated together with a substantial portion of methane. This cooled gas then can be utilized in dephlegmating the distillation in the rectification tower 58 to completely demethanize the condensed hydrocarbons of the coke oven gas.

The condensed rectified hydrocarbons oi the coke oven gas flow through the line 86, through an expansion valve 94, into the top of the evaporator 28. The liquid leaving the bottom of the rectifier 58 is under considerable pressure, that is from 13 to 25 atmospheres depending upon the method of operation of the tower. In the evaporator the liquid is expanded and the temperature reduced. The pressure is reduced to three to ten atmospheres. This expanded liquid hydrocarbon mixture passes in heat interchange relation to the raw gas which is introduced through the line 26 and assists in cooling this gas to the point where it may be passed through the line 34 into the interchanger 38. The expanded liquid-vapor mixture leaves the bottom of the evaporator 28 and flows through a line 96, into the mid portion of a rectifying tower 98.

The rectification oi the hydrocarbon mixture is controlled by means of liquid ethylene. To accomplish this, ethylene is drawn from a line Ill into a compressor I02 and compressed to aproximately 25 to 30 atmospheres. The compressed gas then passes through an interchanger I04 where it is cooled by interchange with cold low pressure ethylene flowing through the line I00. The cooled compressed ethylene then passes through an interchanger I08 where it is cooled by means of refrigeration ammonia introduced through a line I08 and removed through a line I I0. By means of the compression and cooling in the interchangers I04 and I06, the ethylene is completely liquefied and fiows through a line II2 into a coil I I4 in the base of the rectifying column 98. The liquefied ethylene acts to heat liquid in the rectifier 98 and, in turn, is cooled by heat interchange. The cooled liquid ethylene fiows from the heating coil I I4 through a line II8 into a dephlegmating condenser II8 where it is used ior'refluxing vapors leaving the top of the tower 98. After passing through the condenser II8 the ethylene is expanded through a valve I20 into the top of the rectifying tower 98 with a pressure reduction to approximately 1.5 atmospheres. The amount of ethylene together with the temperature and pressure of the liquid ethylene is utilized for controlling the temperatures of rectification in the tower 98. In the tower 98 ethylene passes overhead through the line I00 and all ethylene which is not utilized in the rectification operation is withdrawn from the system through valved line I22.

The higher boiling point hydrocarbons, such as ethane, propane, propylene, butylene and acetylene are withdrawn from the base of column 98 and pass through a line I24 to the top of evaporator 24. Some liquid hydrocarbons which are condensed by the cooling in evaporator 28 accumulate in the bottom of the evaporator and pass through a line I26 where they are mixed with the liquid flowing through the line I24 and pass together into the top of the evaporator 24. Propane and C4 hydrocarbons are withdrawn from the base of evaporator 24 through valved line I28. Lower boiling point vapors such as propylene, ethane, and acetylene pass out of the top of evaporator 24 through a line I30 and flow into the mid portion of a rectifying tower I32. In order to heat the liquid hydrocarbons reaching the base of the column I32, compressed gas is withdrawn from the line 40 through a line I34 and passed through a heating coil I36 in the base of the column. The heating gas leaves the coil I38 through a line I28 and fiows into the gas line 44 which enters the base of exchanger tower 48. Ethane and acetylene pass out of the top of the column I32 into a dephlegmating condenser I40 where all vapors heavier than ethane and acetylene are condensed and returned to the tower. The ethane and acetylene pass overhead from the condenser through a line I42 into a cooling section I44 in exchanger 46. The cooled mixture of ethane and acetylene is removed from the base of the exchanger 48 through a line I46. The temperature of the condenser I40 is controlled by means of cold noncondensed gas'leaving the base of interchanger 38 and flowing through a valved line I48 into the top central portion I50 of the interchanger 48. The cooled gas passes through a valved line I52 into condenser I40 and leaves the condenser through a line I54 where it connects with the line I48 at the opposite side of a valve I56. The non-condensible gases which fiow through the central portion iii) of interchanger 46 leave the bottom of the interchanger through a line I58 and may be conducted through this line to the point of utilization. This gas is composed of a mixture of hydrogen, nitrogen, carbon monoxide and methane and has a comparatively high B. t. u. value so that it may be used for heating purposes. Furthermore the gas may be treated for the separation of hydrogen therefrom.

Propylene is removed from the base of the rectifying column I32 and passes through a line I68 and control valve l6! into an outer section I62 of exchanger 46. After giving up its cold to the incoming compressed gas, it leaves the base of the exchanger 46 through a line I64 and constitutes one of the main products to be recovered.

The methane passing out of the top of the condenser 18 of the rectifying tower 58 is substantially pure. This methane is cold and instead of being passed through the expansion engine 92, may pass through a line I66 which passes through interchanger 38 and interchanger 46 in order to recuperate the low temperature of the methane. After passing through the interchanger 46, the line I66 emerges from the bottom of the interchanger and passes to a point of storage or use of methane.

It will be seen that, by the above arrangement of apparatus, the compressed cooled coke oven gas may be liquefied and rectified in a system' with an expansion engine to provide the cooling for the liquefaction and the demethanizing of the liquid products. The only external cooling medium required is that which is required for liquefying ethylene that is used in rectifying the higher boiling hydrocarbons condensed from the gas in order to separate a pure ethylene.

The preferred form of the invention having been thus described, what is claimed as new is:

I claim:

1. A method of separating olefines from fuel gas containing methane and higher boiling paraflins, ethylene and propylene comprising: compressing the gas, cooling the gas and condensing the higher boiling point constituents therein, separating the gas from the condensate, rectifying the condensate to remove methane overhead and to separate an olefine mixture as a base cut, expanding the separated gas and methane adiabatically to cool the gas, utilizing the cooled gas and methane for controlling the temperatures for said gas-condensate separation and said condensate demethanization, rectifying the demethanized olefine mixture to take overhead an ethylene fraction and a base cut of hydrocarbons having C2 to C4 carbon atoms to the molecule, evaporating the base cut to separate C2 hydrocarbons therefrom and rectifying the C3 and C4 hydrocarbon mixture to separate propylene therefrom.

2. A method of separating olefines from fuel gas containing methane and higher boiling paramns, ethylene and propylene comprising: compressing the gas, cooling the gas sufficiently to condense the higher boiling point hydrocarbons therein and part of the methane, separating the gaseous products from the condensate, rectifying the condensate to separate methane overhead from an olefine base cut, expanding said gaseous products and methane adiabatically to cool the products and utilize the work therefrom, utilizing the cooled products for condensing and rectifying the higher boiling point hydrocarbon products, evaporating the higher boiling point hydrocarbons to cool compressed raw gas and rectifying the evaporated higher boiling point hydrocarbons to separate ethylene therefrom as an overhead cut.

3. A method of separating oleflnes from coke oven gas containing methane and higher boiling paraflins, ethylene and propylene comprising: compressing the gas, cooling the gas sufficiently to condense the higher boiling point hydrocarbons therein and part of the methane, separating the uncondensed gases from the condensate, rectifying the condensate to separate methane overhead from an olefine base cut, expanding said uncondensed gases and methane adiabatically to cool the products, utilizing the cooled expanded products for condensing and rectifying the higher boiling point hydrocarbons, evaporating the higher boiling point hydrocarbons to cool compressed raw gas, rectifying the evaporated higher boiling point hydrocarbons to separate ethylene therefrom as an overhead cut and rectifying the remaining hydrocarbons to separate propylene from the lower boiling point hydrocarbons.

4. The method defined in claim 2 in which ethylene is liquefied and the liquid ethylene is used to control the temperatures in the rectification of the evaporated higher boiling point hydrocarbons.

5. The method defined in claim 2 in which ethylene is liquefied by compression and external cooling and mixed with the evaporated higher boiling point hydrocarbons to provide a temperature control for rectification of said hydrocarbons.

6. The method defined in claim 1 in which the gas being treated is divided and cooled by heat interchange with the adiabatically expanded residue gas and the evaporated higher boiling point hydrocarbon liquid products.

7. The method defined in claim 1 in which the gas being treated is divided into three parts and cooled sufilciently to condense the higher boiling point hydrocarbons by heat interchange with (l) adiabatically expanded discard gas; (2) evaporated higher boiling point hydrocarbon liquid products; and (3) the hydrocarbons in the condensate rectification step.

8. The method defined in claim 2 in which a portion of the compressed raw gas is passed in indirect heat exchange relation with the hydrocarbon condensate being rectifled to control the rectification temperature to demethanize the condensate.

9. The method defined in claim 3 in which the rectification of said remaining hydrocarbons has its base temperature controlled by raw incoming compressed gas and its reflux temperature controlled by the expanded residue gas.

10. The method defined in claim 3 in which the rectification of said remaining hydrocarbons comprising propylene, ethane and ethylene, is carried out so as to take ethane and acetylene as an overhead cut and propylene as a base cut.

11. In an apparatus for recovering olefines from coke oven gas the combination comprising: a rectifying column having a series of heat interchange members distributed throughout the ma: jor portion of the height of the column, means to circulate compressed coke oven gas through the interchange chambers in series to add heat to the liquid being rectified, a heat exchanger connected with said members, an expansion valve in said connection to release the pressure on gas entering the heat exchanger, bailles in said exchanger to aid. in separating gases and liquids from vapors therein, an expansion engine connected with the top of the column for adiabatically expanding uncondensed gases leaving the top'of the column to cool the gases, means to conduct the cooled expanded gases through the heat exchanger to condense portions of the pressure released gases entering therein, means for conducting condensate from the heat interchanger to the upper portion of the rectifying column, a reflux condenser at the top of the column, means for circulating the cooled uncondensed gases and vapors from the exchanger through the condenser in indirect heat interchange relationship to the vapors and gases passing therethrough, the pressure control of the expansion valve and the expansion engine being arranged to condense all hydrocarbons having more than one carbon atom to the molecule while allowing methane, hydrogen, nitrogen and carbon monoxide to pass out of the top of the column.

12. An apparatus for separating olefines from gas containing hydrogen, nitrogen, carbon monoxide and methane, together with higher boiling point hydrocarbons comprising: a rectification column closed for operation under pressure, a heat interchanger for cooling and rectifying gas to be rectified, means in the interchanger for separating gas from liquid hydrocarbons formed therein, means to conduct liquid hydrocarbons from the interchanger to the upper portion of the column, a reflux condenser connected with the top oi the column, means to withdraw hydrocarbons having a higher boiling point than methane from the base of the column, an expansion engine for expanding non-condensed gases leaving the top of the column to cool the gases, means to pass the cooled expanded gases through the interchanger, means to pass the cooled gases separated in the interchanger through the condenser in indirect heat exchange relationship to vapors passing through the condenser from said column, means for controlling the pressure of the gas and vapors in the interchanger, said expansion engine being controllable to control the temperature of the non-condensed gases entering the interchanger to provide gases for cooling the condenser to a temperature at which methane will pass through the condenser to the expansion engine at such a rate that methane will not leave the bottom-of the column with the higher boiling point hydrocarbons.

PIERRE EVAN HAYNES.

. file of this patent:

UNITED STATES PATENTS Name Date Schuftan Jan. 2'7, 1942 Number 

1. A METHOD OF SEPARATING OLEFINS FROM FUEL GAS CONTAINING METHANE AND HIGHER BOILING PARAFFINS, ETHYLENE AND PROPYLENE COMPRISING: COMPRESSING THE GAS, COOLING THE GAS AND CONDENSING THE HIGHER BOILING POINT CONSTITUENTS THEREIN, SEPARATING THE GAS FROM THE CONDENSATE, RECTIFYING THE CONDENSATE TO REMOVE METHANE OVERHEAD AND TO SEPARATE AN OLEFINE MIXTURE AS A BASE CUT, EXPANDING THE SEPARATED GAS AND METHANE ADIABATICALLY TO COOL THE GAS, UTILIZING THE COOLED GAS AND METHANE FOR CONTROLLING THE TEMPERATURES FOR SAID GAS-CONDENSATE SEPARATION AND SAID CONDENSATE DEMETHANIZATION, RECTIFYING THE DEMETHANIZED OLEFINE MIXTURE TO TAKE OVERHEAD AN ETHYLENE FRACTION AND A BASE CUT OF HYDROCARBONS HAV- 